Occurrence of Multidrug-Resistant and Toxic-Metal Tolerant Enterococci in Fresh Feces from Urban Pigeons in Brazil

Enterococcus are emerging as important putative pathogens resistant to chemicals that are widely released into the environment, and urban pigeons might act as a natural reservoir contributing to the spread of resistant strains. This study aimed to evaluate the occurrence of Enterococcus in pigeon feces and their antimicrobial and toxic metal susceptibility. Bacteria were isolated and identified from 150 fresh feces by phenotypic and genetic techniques. Antimicrobial and toxic metal susceptibility was determined by the agar dilution method, and the multiple antibiotic resistance index (MAR) was calculated. Out of 120 isolates, no resistance was observed against penicillin and vancomycin, but was observed against gentamicin (55.8%), chloramphenicol (21.7%), tetracycline (13.3%), ciprofloxacin (8.4%) and rifampin (2.5%). 18.3% presented a MAR index ≥0.2, ranging between 0.14 to 0.57, indicating resistance to more than one antimicrobial. All samples were tolerant to >1024 µg mL⁻¹ zinc and chromium. Minimal inhibitory concentration (MIC) of 1,024 µg mL⁻¹ was observed for copper (100%) and nickel (71.4%). Mercury inhibited 88.4% at 32 µg mL⁻¹ and the MIC for cadmium ranged from 0.125-128 µg mL⁻¹. Since pigeons were found to harbor drug-resistant Enterococcus, our data support that their presence in the urban environment may contribute to the spread of resistance, with an impact on public health.